As someone has pointed out in the post's comments, there's the Wombat ADB-USB converter as an alternative. Doesn't look as good, but requires no battery or other power supply. IIRC, it does distinguish between left and right Shift/Command/Option keys. Quickly looking at the product page I realize that it even converts both ways, so you can also use it to attach your USB keyboard to your ADB Mac or NeXT.
On ADB keyboards with two Command keys, both keys result in the same code being sent — so it is impossible for a converter to distinguish between them.
I have seen that on the AEKII the two keys' switches are even electrically connected on the circuit board.